1. Field of Invention
The invention is concerned with a non-rotating air cooled aerofoil component (referred to as a nozzle guide vane or stator) in a gas turbine engine.
2. Description of Related Art
It is now common practice for selected gas turbine engine components, especially in the turbine section, to be internally air cooled by a supply of air bled from a compressor offtake. Such cooling is necessary to maintain component temperatures within the working range of the materials from which they are constructed. Higher engine gas temperatures have led to increased cooling bleed requirements resulting in reduced cycle efficiency and increased emissions levels. To date, it has been possible to improve the design of cooling systems to minimize cooling flow at relatively low cost. In the future, engine temperatures will increase to levels at which it is necessary to have complex cooling features to maintain low cooling flows.
FIG. 1 illustrates the main sections of a gas turbine engine. The overall construction and operation of the engine is of a conventional kind, well known in the field, and will not be described in this specification beyond that necessary to gain an understanding of the invention. The engine comprises: a fan section 10; a low pressure compressor 11 and a high pressure compressor 12; a combustor section 13 and a nozzle guide vane array 17; and high pressure turbine 14, an intermediate pressure turbine 15 and a low pressure turbine 16. Air enters the engine via the fan section 10. The air is compressed and moves downstream to the low and high pressure compressors 11, 12. These further pressurize the air, a proportion of which enters the combustion section 13, the remainder of the air being employed elsewhere, including the air cooling system. Fuel is injected into the combustor airflow, which mixes with air and ignites before exhausting out of the rear of the engine via the low, intermediate and high pressure turbines 14, 15, 16. Air not used for combustion is used, in part, for cooling of components such as, byway of non-limiting example, the nozzle guide vanes 17 and turbines 14, 15, 16.
A typical cooling style for a nozzle guide vane for a high pressure turbine is described in UK Patent GB 2,163,218, illustrations of which are shown below, in FIGS. 2 and 3. Essentially, the aerodynamic profile is bounded by a metallic wall of a thickness sufficient to give it structural strength and resist holing through oxidation. Where necessary, the opposing walls are xe2x80x9ctiedxe2x80x9d together giving additional strength. In many cases the compartments formed by these wall ties (or partitions) are used to direct and use the cooling air. For example, in FIG. 2 the cooling air flows up the middle before exiting towards the trailing edge.
The main problem with such a system is that there is a need to keep the metallic surface below a certain temperature to obtain an acceptable life. As the engine temperature increases the surface area exposed to the hot gas requires more cooling air to achieve the temperature required. Ultimately the benefits expected by increasing the gas temperature will be outweighed by the penalty of taking additional cooling bleed.
The present invention seeks to provide a nozzle guide vane that uses less cooling air than current state of the art designs and with improved structural integrity and life.
According to the present invention there is provided an air cooled component provided with an internal air cooling system comprising an internal cavity and at least one side wall chamber formed in the wall of the component, having at least one air entry aperture for admitting cooling air into the side wall chamber and at least one air exit aperture for exhausting air from the side wall chamber, and the internal cavity is divided into at least two compartments which are arranged in flow sequence by communication through the side wall chambers, wherein at least one of the side wall chambers is sub-divided into a plurality of cells in parallel flow relationship and each of the cells has at least one air entry aperture and at least one air exit aperture.
An exemplary embodiment of an air cooled component according to this invention provides an air cooling system comprising an internal cavity and a plurality of side wall chambers formed in the wall of the component, the internal cavity capable of being divided into at least two compartments, the compartments of the internal cavity and at least one of the side wall chambers arranged in a single overall flow sequence from the leading edge of the component to the trailing edge of the component by communication of air between progressively downstream compartments of the internal cavity through at least one of the side wall chambers, wherein at least one of the side wall chambers is sub-divided into a plurality of cells in parallel flow relationship and each of the cells has at least one air entry aperture and at least one air exit aperture, the at least one air entry aperture configured such that air passing through the at least one air entry aperture into a first side wall chamber will impinge on the inner surface of the outer wall of the component to provide impingement and convection cooling, and the at least one air exit aperture configured to exhaust air to ambient air surrounding the component through an outer wall of the component or at least one compartment of the internal cavity such that the air may be delivered to a second side wall chamber before being exhausted to the ambient air surrounding the component through an outer wall of the component, the exhausted air providing an outer surface cooling film.